Combines are, of course, used to harvest crops and also to separate the edible parts of a crop from the rest of it. By the use of various attachments, a combine may be used for harvesting small grain such as wheat and rice; for harvesting edible beans and soy beans; for harvesting corn for silage in which the husks are removed, leaving the cobs with the grain intact; or for husking and shelling corn so that the grain is removed from the cobs.
Regardless of the purpose for which a combine is used, it delivers the usable end product to grain tanks and drops a large amount of residual material onto the ground where it is plowed into the soil. When small grain is combined the residue consists principally of chaff, together with a small amount of grain which has not been picked up for feeding into the grain tank. Straw is usually discharged separately, and may be saved for use as bedding or may be discharged onto the ground, either in long pieces or after passing through an auxiliary straw chopper.
In bean harvesting, the beans are delivered to the grain tank, while stems, leaves and other parts, together with some beans not picked up for transfer to the grain tank, constitute the residue.
When corn is harvested and processed for silage, the residue consists principally of husks, together with finer parts of the plants. In the harvesting and shelling of corn, the residue includes small material plus the cobs and the husks.
In all cases, the residue normally returned to the soil by a combine contains substantial quantities of usable material, much of which is even usable as animal feed.